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An electrical device is powered by a battery. The device includes
transition phase determining circuitry operatively connected to the
battery to determine that the battery has entered a transition phase
based on the occurrence of a change in direction of current flowing
through the battery. Battery capacity determining circuitry is
operatively connected to the transition phase determining circuitry and
configured to determine, in response the transition phase determining
circuitry determining that the battery is in the transition phase, a
capacity of the battery based on a transition phase battery capacity
model of capacity-vs.-voltage. The transition phase determining circuitry
is further configured to determine an end of the transition phase based
on the transition phase battery capacity model and a non-transition
battery capacity model of capacity-vs.-voltage yielding the same capacity
value for a given measured voltage of the battery.

Inventors:

Ahmed; Farhad; (Ottawa, CA); Fu; Runbo; (Kanata, CA)

Assignee:

RESEARCH IN MOTION LIMITEDWaterlooCA

Serial No.:

181777

Series Code:

13

Filed:

July 13, 2011

Current U.S. Class:

324/427

Class at Publication:

324/427

International Class:

G01N 27/416 20060101 G01N027/416

Claims

1. An electrical device powered by a battery, comprising: voltage reading
circuitry configured to monitor the voltage of a power source connector
that is charging the battery; transition phase determining circuitry
operatively connected to the voltage reading circuitry to determine that
the battery has entered a transition phase based on sensing an abrupt
change in the voltage; and battery capacity determining circuitry
configured to determine, in response to the transition phase determining
circuitry determining that the battery is in the transition phase, a
capacity of the battery based on a transition phase battery capacity
model that defines the battery's capacity as a function of the battery's
voltage; the transition phase determining circuitry being further
configured to determine that the transition phase has ended based on the
lapse of a predetermined time period from the start of the transition
phase; and the transition phase battery capacity model being determined
from both a non-transition battery capacity charge model and a
non-transition battery capacity discharge model, all three models
defining the battery's capacity as a function of its voltage.

2. The electrical device of claim 1 wherein the abrupt change is from 0V
to a predetermined voltage value or from a predetermined voltage value to
0V.

3. The electrical device of claim 1 wherein the battery capacity
determining circuitry is further configured to cease to base the capacity
determination on the transition phase battery capacity model, in response
to the transition phase determining circuitry determining the end of the
transition phase.

4. The electrical device of claim 1 wherein the battery capacity
determining circuitry is further configured to determine the battery
capacity based on a non-transition phase battery capacity model, in
response to the transition phase determining circuitry determining the
end of the transition phase.

5. The electrical device of claim 1 wherein a capacity value of the
transition phase model for each given voltage is calculated as a function
of two capacity values yielded by the charge model and discharge model
for the given voltage.

6. The electrical device of claim 1 wherein a capacity value of the
transition phase model for each given voltage is determined
experimentally.

7. The electrical device of claim 1 wherein the electrical device is a
mobile communication device.

8. An electrical device powered by a battery, comprising: voltage reading
circuitry configured to monitor the voltage of a power source connector
that is charging the battery; transition phase determining circuitry
operatively connected to the voltage reading circuitry to determine that
the battery has entered a transition phase based on sensing an abrupt
change in the voltage; and battery capacity determining circuitry
configured to determine, in response to the transition phase determining
circuitry determining that the battery is in the transition phase, a
capacity of the battery based on a transition phase battery capacity
model that defines the battery's capacity as a function of the battery's
voltage; the transition phase determining circuitry being further
configured to determine that the transition phase has ended based on the
battery voltage having changed by a predetermined voltage value from the
battery voltage at the start of the transition phase; and the transition
phase battery capacity model being determined from both a non-transition
battery capacity charge model and a non-transition battery capacity
discharge model, all three models defining capacity as a function of
voltage for the battery.

9. The electrical device of claim 8 wherein the abrupt change is from 0V
to a predetermined voltage value or from a predetermined voltage value to
0V.

10. The electrical device of claim 8 wherein the battery capacity
determining circuitry is further configured to cease to base the capacity
determination on the transition phase battery capacity model, in response
to the transition phase determining circuitry determining the end of the
transition phase.

11. The electrical device of claim 8 wherein the battery capacity
determining circuitry is further configured to determine the battery
capacity based on a non-transition phase battery capacity model, in
response to the transition phase determining circuitry determining the
end of the transition phase.

12. The electrical device of claim 8 wherein a capacity value of the
transition phase model for each given voltage is calculated as a function
of two capacity values yielded by the charge model and discharge model
for the given voltage.

13. The electrical device of claim 8 wherein a capacity value of the
transition phase model for each given voltage is determined
experimentally.

14. The electrical device of claim 8 wherein the electrical device is a
mobile communication device.

15. An electrical device powered by a battery, comprising: voltage
reading circuitry configured to monitor the voltage of a power source
connector that is charging the battery; transition phase determining
circuitry operatively connected to the voltage reading circuitry to
determine that the battery has entered a transition phase based on
sensing an abrupt change in the voltage; and battery capacity determining
circuitry configured to determine, in response to the transition phase
determining circuitry determining that the battery is in the transition
phase, a capacity of the battery based on a transition phase battery
capacity model that defines the battery's capacity as a function of the
battery's voltage; the transition phase determining circuitry being
further configured to determine an end of the transition phase based on
the transition phase battery capacity model and a non-transition battery
capacity model of capacity-vs.-voltage yielding the same capacity value
for a given measured voltage of the battery.

16. The electrical device of claim 15 wherein the abrupt change is from
0V to a predetermined voltage value or from a predetermined voltage value
to 0V.

17. The electrical device of claim 15 wherein the battery capacity
determining circuitry is further configured to cease to base the capacity
determination on the transition phase battery capacity model, in response
to the transition phase determining circuitry determining the end of the
transition phase.

18. The electrical device of claim 15 wherein the battery capacity
determining circuitry is further configured to determine the battery
capacity based on a non-transition phase battery capacity model, in
response to the transition phase determining circuitry determining the
end of the transition phase.

19. The electrical device of claim 15 wherein a capacity value of the
transition phase model for each given voltage is calculated as a function
of two capacity values yielded by the charge model and discharge model
for the given voltage.

20. The electrical device of claim 15 wherein the electrical device is a
mobile communication device.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation of U.S. application Ser. No. 12/689,914,
filed Jan. 19, 2010, which is a continuation of U.S. application Ser. No.
11/945,765, filed Nov. 27, 2007 (now U.S. Pat. No. 7,676,335), which is a
continuation of U.S. application Ser. No. 11/499,291, filed Aug. 4, 2006
(now U.S. Pat. No. 7,317,996), which is a continuation of U.S.
application Ser. No. 10/982,461, filed Nov. 5, 2004 (now U.S. Pat. No.
7,107,161), all the above applications hereby incorporated herein by
reference.

TECHNICAL FIELD

[0002] This application relates generally to batteries, and more
particularly to reporting the capacity of a battery.

BACKGROUND

[0003] Many mobile computing and communicating devices rely upon standard
battery cells for providing power on which to operate. Though disposable
battery cells, such as alkaline cells, are a well-known and reliable
technology, it is common in such mobile devices to employ rechargeable
battery cells. These rechargeable batteries depend on a number of known
cell types, including Ni-Cad, Ni-MH, and Li-Ion cells. All these cells
are known to those of skill in the art, as are some of their
deficiencies. One of the known deficiencies of the above mentioned
rechargeable battery cells is related to the fact that each battery has a
finite life span that can be measured in terms of recharge cycles. The
process of charging and discharging the cell damages the cell's charge
storage capabilities, causing the stored potential, which is typically
measured in mA-hours, to decrease over the life of the battery. As the
ability to store charge decreases, so does the battery's utility. The
life of the battery can be drastically curtailed by improperly charging,
or over discharging the battery. As a result of these deficiencies, it is
crucial that a user be able to determine the capacity of a battery both
prior to and during the usage.

[0004] A state of the art technique for battery capacity reporting relies
on the coulomb counter. The principle of operation involved in coulomb
counting is computing the difference between the coulombs injected into a
battery and the coulombs taken out of the battery. The capacity of the
battery is then reported by comparing the coulomb count relative to a
reference coulomb count value that corresponds to maximum battery
capacity. For instance, if the coulomb count of a battery is half of the
reference value, the battery capacity is reported to be 50 percent.
Although the coulomb counter addresses battery capacity reporting, it may
have several problems. First, the reported capacity may not be meaningful
if an accurate reference coulomb count value corresponding to maximum
battery capacity is not known. Furthermore, with a coulomb counter it may
be difficult to keep an accurate reference coulomb count, particularly
when battery capacity decreases over the lifetime of the battery. Further
still, with a coulomb counter it may be necessary to know the current
battery capacity before beginning the coulomb count.

[0005] A limitation of the coulomb counting principle is that it may not
be applicable to reporting the capacity of a battery of initially unknown
battery capacity: if the capacity of a battery is to be reported using
the coulomb count system and method, the battery may have to be taken
from its unknown capacity state to either a fully charged 100% battery
capacity state or to a fully discharged 0 percent capacity state before
the coulomb count can be used. Because the state of the battery is
unknown at a certain point, the only way to charge the battery to 100%
capacity is to constantly provide charge over an extended length of time.
This can result in an overcharging of the cell, which is known to damage
the storage capability of the cell. Conversely, to guarantee that the
cell is at 0% capacity, the cell must be completely discharged.
Rechargeable batteries are possibly permanently damaged by being overly
discharged.

[0006] Further practical limitations exist with coulomb counting
techniques. In practice, coulomb counting works by applying integration
over time. The presence of an offset in a coulomb counter may result in
the inaccuracy of the coulomb count. This applies even to batteries with
an assumed initially known battery capacity, and is compounded with every
recharge cycle. This may be especially true if the battery needs to be
used for a long period of time between opportunities to reset the coulomb
counter. For instance, in a battery that needs to be used for 3 weeks
between charges, even small offsets with each charge cycle may accumulate
to become large inaccuracies in reported capacity.

[0007] Other known existing techniques of battery capacity reporting are
primarily based on measuring battery voltage.

[0008] Batteries have known characteristic charge and discharge curves.
FIG. 1 illustrates a charge curve model 130 and a discharge curve model
140 for a battery. These curves relate battery voltage 110 to capacity
percentage 120 for a rechargeable battery. Battery capacity percentage
120 is related to battery voltage 110 in either a discharging state,
shown by the discharge curve model 140, or the charging state shown by
the charge curve model 130. Illustrated is a multiplicity of points such
as point 132 on the charge curve model 130 and point 142 on the discharge
curve. Interpolation can be used to provide capacity values 120 for
voltages 110 that lie between points for which values are known. In
reference to FIG. 1, the relationship between battery voltage 110,
battery charge state and capacity 120 is illustrated by two curve models
130,140. The first curve model 130 corresponds to a positive battery
charge current or battery charging state, and the second curve model 140
corresponds to a negative battery charge current or battery discharging
state.

[0009] When the battery is in a charging state, a charge curve
corresponding to the charging state is utilized. When the battery is in a
discharging state, a discharge curve corresponding to the discharging
state is utilized. The charge and discharge curves are such that given a
battery voltage value and a charge curve or a discharge curve, it is
possible to obtain a corresponding capacity value from the curves.

[0010] Though it is possible to determine the capacity of a battery by
measuring the voltage of the battery and examining the curves, it should
be noted that the existence of two distinct curves presents a problem.
For example, when a battery voltage is 3.8 V and a power source is
plugged into the battery at this time, according to the discharge state
curves, there is an abrupt drop of the reported battery capacity from 52%
to 17%. The reported result is not correct. Actually, a battery enters a
transition phase P1 from discharging to charging when a power source is
plugged in while the battery is discharging. After the transition phase
P1, the battery goes into the charging state. Similarly, when a power
source is removed while charging a battery, for example, at a battery
voltage 3.9V, there is an abrupt rise of the reported battery capacity
from 49% to 71% based on the charging curve and the discharging curve of
FIG. 1. Actually, a battery enters a transition phase P2 from charging to
discharging when a power source is removed while charging the battery.
After the transition phase P2, the battery goes into the discharging
state. Under the above circumstances, the reported result will not be
correct if the discharging curve and the charging curve of FIG. 1 are
used to report the battery capacity in the transition phases.

SUMMARY

[0011] A method includes monitoring the voltage of a power source
connector for charging a battery. A determination is made that the
battery has entered a transition phase based on sensing an abrupt change
in the voltage. In response to determining that the battery is in the
transition phase, a capacity of the battery is determined based on a
transition phase battery capacity model that defines the battery's
capacity as a function of the battery's voltage.

[0012] Preferably, the determination step includes determining that the
battery has entered a transition phase from discharging to charging based
on sensing an abrupt increase in the connector voltage. The determination
step includes determining that the battery has entered a transition phase
from charging to discharging based on sensing an abrupt decrease in the
connector voltage. The method further includes determining that the
transition phase has ended based on the lapse of a predetermined time
period from the start of the transition phase, or based on the battery's
voltage having changed by a predetermined voltage value from the
battery's voltage at the start of the transition phase. The method
further includes determining the transition phase battery capacity model
from both a non-transition battery capacity charge model and a
non-transition battery capacity discharge model, all three models
defining the battery's capacity as a function of the battery's voltage.

[0016] FIG. 4 illustrates an example of a transition battery capacity
model curve for reporting a battery capacity in a transition phase from
discharging to charging.

[0017] FIG. 5 illustrates an example of a transition battery capacity
model curve for reporting a battery capacity in a transition phase from
charging to discharging.

[0018] FIG. 6 is a flowchart illustrating an example method to carry out
step 360 of FIG. 3 according to the transition battery capacity models of
FIGS. 4 and 5.

DETAILED DESCRIPTION

[0019] Generally, the present application provides a method and system for
reporting battery capacity accurately by means of a battery capacity
transition phase model when an event occurs. The event may be the
attachment or disconnection of the battery to a battery charger or power
source, the occurrence of a fault condition such as power failure to the
battery charge when the battery is attached, or the like.

[0020] The battery capacity transition phase model may be described as a
function or may be described through interpolation of values stored in a
look up table or array.

[0021] An example method for reporting battery capacity reports the
battery capacity based on a transition phase battery capacity model
during a transition phase. A transition phase battery capacity model
relevant to the transition phase from discharging to charging and a
transition phase battery capacity model relevant to the transition phase
from charging to discharging are predetermined. Once it is determined
that the battery is in a transition state, a discharging state, or a
charging state, then a transition phase battery capacity model curve, a
discharge curve or a charge curve is selected respectively. A voltage of
the battery is then read, and a battery capacity is determined by using
the selected curve. The transition phase battery capacity model is
preferably a function associated with battery voltage, discharge curve
and charge curve. This function may be expressed as an equation, a set of
equations, a look up table, or the like.

[0023] Alternatively, a plurality of transition phase battery capacity
model curves, discharge curves and charge curves corresponding to a
plurality of battery operating temperatures or a plurality of battery
operating temperature ranges may be provided, so that a corresponding
curve for reporting battery capacity cab be selected based on a current
battery operating temperature to obtain an accurate battery capacity.

[0024] FIG. 2 is a block diagram of a mobile communication device 10 that
may implement a system and method for accurately reporting battery
capacity, as described herein. The mobile communication device 10 is
preferably a two-way communication device having at least voice or data
communication capabilities. The device preferably has the capability to
communicate with other computer systems on the Internet. Depending on the
functionality provided by the device, the device may be referred to as a
data messaging device, a two-way pager, a cellular telephone, a wireless
Internet appliance or a data communication device (with or without
telephony capabilities). It should be understood, however, that battery
capacity reporting and measurement may have applications other than in
the field of mobile communicating and computing devices.

[0025] Where the device 10 is enabled for two-way communications, the
device may incorporate a communication subsystem 11, including a receiver
12, a transmitter 14, and associated components such as one or more,
preferably embedded or internal, antenna elements 16 and 18, local
oscillators (LOs) 13, and a processing module such as a digital signal
processor (DSP) 20. The particular design of the communication subsystem
11 is dependent upon the communication network in which the device is
intended to operate. For example, a device 10 may include a communication
subsystem 11 designed to operate within the Mobitex.TM. mobile
communication system, DataTAC.TM. mobile communication system, General
Packet Radio Service (GPRS) communication subsystem, CDMA communication
system, and iDEN communication system.

[0026] Network access requirements may also vary depending upon the type
of network 19. For example, in the Mobitex.TM. and DataTAC.TM. networks,
mobile devices are registered on the network using a unique personal
identification number or PIN associated with each device. In GPRS
networks however, network access is associated with a subscriber or user
of a device 10. A GPRS device therefore requires a subscriber identity
module, commonly referred to as a SIM card, in order to operate on a GPRS
network. Without a SIM, a GPRS device will not be fully functional. Local
or non-network communication functions (if any) may be operable, but the
device 10 may be unable to carry out functions involving communications
over network 19. When required network registration or activation
procedures have been completed, a device 10 may send and receive
communication signals over the network 19. Signals received by the
antenna 16 through a communication network 19 are input to the receiver
12, which may perform such common receiver functions as signal
amplification, frequency down conversion, filtering, channel selection
and analog-digital conversion. Analog to digital conversion of a received
signal allows complex communication functions, such as demodulation and
decoding, to be performed in the DSP 20. In a similar manner, signals to
be transmitted are processed, including modulation and encoding for
example, by the DSP 20 and input to the transmitter 14 for digital to
analog conversion, frequency up conversion, filtering, amplification and
transmission over the communication network 19 via the antenna 18.

[0027] The DSP 20 not only processes communication signals, but also
provides for receiver and transmitter control. For example, the gains
applied to communication signals in the receiver 12 and transmitter 14
may be adaptively controlled through automatic gain control algorithms
implemented in the DSP 20.

[0028] The device 10 preferably includes a microprocessor 38 which
controls the overall operation of the device. Communication functions,
including at least one of data and voice communications, are performed
through the communication subsystem 11. The microprocessor 38 also
interacts with further device subsystems such as the display 22, flash
memory 24, random access memory (RAM) 26, auxiliary input/output (I/O)
subsystems 28, serial port 30, keyboard 32, speaker 34, microphone 36, a
short-range communications subsystem 40 and any other device subsystems
generally designated as 42.

[0029] Some of the subsystems shown in FIG. 2 perform
communication-related functions, whereas other subsystems may provide
"resident" or on-device functions. Some subsystems, such as keyboard 32
and display 22 for example, may be used for both communication-related
functions, such as entering a text message for transmission over a
communication network, and device-resident functions such as a calculator
or task list.

[0030] Operating system software used by the microprocessor 38 may be
stored in a persistent store such as flash memory 24, which may instead
by a read only memory (ROM) or similar storage element. Discharge curves,
charge curves and transition phase battery capacity models as discussed
below may be pre-stored in memory 24. The operating system, specific
device applications, or parts thereof, may be temporarily loaded into a
volatile store such as RAM 26. Received communication signals may also be
stored to RAM 26.

[0031] The microprocessor 38, in addition to its operating system
functions, enables execution of software applications on the device. A
predetermined set of applications which control basic device operations,
including at least data and voice communication applications for example,
will normally be installed on the device 10 during manufacture. One
example application that may be loaded onto the device is a personal
information manager (PIM) application having the ability to organise and
manage data items relating to the device user such as, but not limited to
e-mail, calendar events, voice mails, appointments, and task items. One
or more memory stores may be available on the device to facilitate
storage of PIM data items on the device. Such PIM application may have
the ability to send and receive data items, via the wireless network. The
PIM data items may be seamlessly integrated, synchronized and updated,
via the wireless network, with the device user's corresponding data items
stored or associated with a host computer system thereby creating a
mirrored host computer on the mobile device with respect to the data
items at least. This may be especially advantageous in the case where the
host computer system is the mobile device user's office computer system.
Further applications may also be loaded onto the device 10 through the
network 19, an auxiliary I/O subsystem 28, serial port 30, short-range
communications subsystem 40 or any other suitable subsystem 42, and
installed by a user in the RAM 26 or a non-volatile store for execution
by the microprocessor 38. Such flexibility in application installation
increases the functionality of the device and may provide enhanced
on-device functions, communication-related functions, or both. For
example, secure communication applications may enable electronic commerce
functions and other such financial transactions to be performed using the
device 10.

[0032] In a data communication mode, a received signal such as a text
message or web page download is processed by the communication subsystem
11 and input to the microprocessor 38, which may further process the
received signal for output to the display 22, or alternatively to an
auxiliary I/O device 28. A user of device 10 may also compose data items
such as email messages for example, using the keyboard 32, which may be a
complete alphanumeric keyboard or telephone-type keypad, in conjunction
with the display 22 and possibly an auxiliary I/O device 28. Such
composed items may then be transmitted over a communication network
through the communication subsystem 11.

[0033] For voice communications, overall operation of the device 10 is
substantially similar, except that received signals may be output to a
speaker 34 and signals for transmission may be generated based on an
input received through a microphone 36. Alternative voice or audio I/O
subsystems such as a voice message recording subsystem may also be
implemented on the device 10. Although voice or audio signal output may
be accomplished primarily through the speaker 34, the display 22 may also
be used to provide an indication of the identity of a calling party, the
duration of a voice call, or other voice call related information for
example.

[0034] The serial port 30 in FIG. 2 may be implemented in a personal
digital assistant (PDA)-type communication device for which
synchronization with a user's desktop computer may be desirable, the
serial port 30 may enable a user to set preferences through an external
device or software application and extend the capabilities of the device
by providing for information or software downloads to the device 10 other
than through a wireless communication network. The alternate download
path may for example be used to load an encryption key onto the device
through a direct and thus reliable and trusted connection to thereby
enable secure device communication.

[0035] A short-range communications subsystem 40 may be included to
provide for communication between the device 10 and different systems or
devices, which need not necessarily be similar devices. For example, the
subsystem 40 may include an infrared device and associated circuits and
components or a Bluetooth.TM. communication module to provide for
communication with similarly-enabled systems and devices.

[0036] A charging subsystem 44 may be included to provide power for the
device 10 and different subsystems or devices. For example, the charging
subsystem 44 may determine the presence of detachable power source device
46 and associated circuits, such as an AC adapter, USB cable, or car
adapter to provide power for the device and to charge battery 48.
Additionally, charging subsystem 44 may determine the absence of power
source device 46, and consequently obtain power for the device 10 from
battery 48. Generally speaking, when power source device 46 is
disconnected to charging subsystem 44 and battery 48 powers device 10
alone, battery 48 is said to be in a discharging state. Conversely, when
power source device 46 is connected to charging subsystem 44 and powers
device 10, and charging subsystem 44 charges battery 48, battery 48 is
said to be in a charging state. Actually, there is a transition phase
from charging to discharging before battery 48 enters into a discharging
state from a charging state, and a transition phase from discharging to
charging before battery 48 enters into a charging state from a
discharging state. The present application describes an example system
and method for reporting the capacity of a battery, such as battery 48,
during transition phases.

[0037] The battery capacity reported is a function of several factors,
including battery voltage, battery charging current, and so on. The
relationship between battery voltages, battery charging currents, and
battery capacity is modelled using charge curves such as those
illustrated in FIG. 1. Therefore, before describing embodiments of the
method and system in detail, several concepts will be defined for greater
certainty.

[0038] As used in this description and in the appended claims, the battery
voltage is defined as the voltage differential between positive and
negative terminals of the battery.

[0039] As used in this description and in the appended claims, battery
charging current is defined as a current flowing into the battery.
Battery charging current is capable of taking on a signed value, with a
positive value meaning current being delivered into the battery and a
negative value meaning current drawn out of the battery.

[0040] As used in this description and in the appended claims, a state of
a battery is one of a charging state corresponding to a positive battery
charging current value and a discharging state corresponding to a
negative battery charging current value. A discharge curve model or a
charge curve model is defined as the relationship between battery
voltage, battery charging current and capacity so that given battery
voltage and battery charging current, capacity can be determined by
applying the capacity curve model.

[0041] When there is a change in the direction of a battery charging
current or a change in the sign of a battery charging current value, for
example, if the change is from delivering into a battery to drawing out
of the battery or from a positive current value to a negative current
value, it is determined that a battery enters a transition phase from a
charging state; if the change is from drawing out of the battery to
delivering into the battery or from a negative current value to a
positive current value, it is determined that a battery enters a
transition phase from a discharging state. Alternatively, as shown in
FIG. 2, by monitoring a battery's power source connector, when there is
an abrupt voltage change from 0V to a predetermined voltage value, it is
determined that the battery 48 enters into a transition phase from
discharging to charging. When there is an abrupt voltage change from the
predetermined voltage value to 0V, it is determined that the battery 48
enters into a transition phase from charging to discharging. It should be
understood that there are various methods to determine if a battery is in
a transition phase or in a charging state or discharging state.

[0042] Referring to FIGS. 1 and 2, the example method may use a system,
such as system 10 of FIG. 2, including a charging subsystem 44, to assist
in determining values for the battery voltage 110 and battery capacity
120. The charging current can be used to determine the state and select
either one of the curve models 130, 140. The charging subsystem 44 may be
capable of performing several operations such as constant current
charging operation and constant voltage charging operation.

[0043] FIG. 3 illustrates an example method for reporting battery
capacity. At step 305, a battery identification (ID) is provided to
identify the type of the battery. At step 310, a discharge curve model,
such as 140, corresponding to the battery ID is provided. At step 320, a
charge curve model, such as 130, corresponding to the battery ID is
provided. At step 330, with respect to the battery ID, a transition phase
battery capacity model F1 corresponding to a transition phase P1 from
discharging to charging and a transition phase battery capacity model F2
corresponding to a transition phase P2 from charging to discharging are
provided for reporting battery capacities during the transition phases P1
and P2. A transition phase P1 and a transition phase P2 are defined and
provided. Models F1 and F2 may have a variety of forms from simple to
complicated. More complicated models may more accurately report the
capacity with less error at the expense of higher computational
complexity. Models F1 and F2 may be of different or the same form.

[0044] Models F1 and F2 may be predetermined by experimentation. A
transition phase P1 from discharging to charging and a transition phase
P2 from charging to discharging are defined by means of a battery voltage
change amount or by means of time change amount from the point where the
charging or discharging state changes, that is, from the point when a
battery is connected to a power source or a battery is disconnected from
a power source. A transition phase is deemed to be over after a defined
transition phase. For example, if a battery voltage change amount is used
to define the transition phase, the voltage change amount may range from
0.05V to 0.3V. Similarly, if a time change amount is used to define the
transition phase, the time change amount may range from 0.5 hours to 3
hours when the system is in a standby mode. Alternatively, if a battery
capacity determined from a transition phase battery capacity model F1
corresponding to a transition phase from discharging to charging and a
battery capacity determined from a charge curve model are same, the
transition phase from discharging to charging is deemed to be over.
Similarly, if a battery capacity determined from a transition phase
battery capacity model F2 corresponding to a transition phase from
charging to discharging and a battery capacity determined from a
discharge curve model are same, the transition phase from charging to
discharging is deemed to be over.

[0045] After the transition phase, a battery enters the charging state or
the discharging state. The criterions of modeling capacity curves during
the transition phase are to make them approach the actually measured
capacity curves so as to minimize the capacity reporting error. The
transition phase battery capacity model corresponding to the transition
phase P1 and the transition battery capacity model corresponding to the
transition phase P2 may be described by two functions. The transition
phase battery capacity functions may be determined based on the discharge
curve model 140 and the charge curve model 130 of FIG. 1, as described
below with reference to FIG. 4.

[0046] At step 340, battery voltage is provided to determine battery
capacity subsequently. At step 350, battery current is provided. By
detecting a change in the direction or a change in sign of battery
current value, it may be determined if the battery is in a transition
phase, in a discharging state or in a charging state. At step 355, the
battery temperature is measured. At step 360, the transition phase
battery capacity model corresponding to the transition phase P1 or the
transition phase battery capacity model corresponding to the transition
phase P2 is applied to determine a battery capacity based on a battery
voltage. Step 360 is described in detail below with reference to FIG. 6.

[0047] FIG. 4 illustrates an example transition battery capacity model
curve for reporting a battery capacity in a transition phase from
discharging to charging. In this example, the transition battery capacity
model is described by a transition phase battery capacity function.

[0048] In FIG. 4, a battery 48 is assumed to be initially discharging 140
and at voltage 110 of 3.75V corresponding to point 442. Consequently, a
37% capacity is determined. Next, the battery enters the charging state,
for instance if the power source 46 of FIG. 2 is connected while the
battery is in use.

[0049] A battery that has been discharging and has a voltage reading of
3.75V can be determined to be 37% full by directly mapping from the
initial discharge curve, corresponding to a discharging state. If a power
source 46 is plugged in at this point, then the battery's capacity would
erroneously be determined to be 10% full, according to the point where
3.75V maps on the new charging curve model 130 corresponding to a
charging state. If that value were reported directly, then the user would
see an incorrect capacity. Actually, the battery takes some time to reach
to the charging curve model 130; that is, there is a transition phase P1
from discharging to charging. A measured relationship curve 440 between
capacity and voltage during a transition phase P1 from discharging to
charging starts at point 442 corresponding to the discharging curve 140
and ends at point 434 corresponding to the charging curve model 130. A
transition battery capacity function F1 corresponding to a transition
phase P1 from discharging to charging is predetermined for reporting the
battery capacity during the transition phase P1, and the determined
function F1 curve 450 approaches the measured relationship curve 440. A
transition phase battery capacity function F1 curve 450 starts at point
442 and ends at point 432. It can be seen from FIG. 4 that the curve 450
closely matches the behaviour of the measured relationship curve 440 such
that any discrepancy in capacity is within 6%. Various transition phase
battery capacity functions F1 may be used as long as the capacity
reporting error is less than measured error 6%. More complicated
functions may lead to more accurate battery capacity values and less
capacity reporting error such as 2%, 1% or less. The following
description concerns an example transition phase battery capacity
function F1 based on a discharge curve and a charge curve.

[0050] In order to create a transition phase capacity function F1
corresponding to a transition phase P1 from a discharging state to a
charging state, a real transition phase curve is determined through
measurement, and then a function with a curve approaching the real
transition phase curve is determined as a function F1 for a transition
phase P1 from a discharging state to a charging state. Model F1 may be
varied with different complexity. More complicated models may more
accurately report the capacity with less error at the expense of higher
computational complexity.

[0051] A transition phase battery capacity function F1 corresponding to a
transition phase P1 from a discharging state to a charging state may be
formulated as:

[0053] .DELTA.V defines the transition phase P1 which is a battery voltage
change amount between an end voltage and a start voltage in the
transition phase P1; that is, .DELTA.V=V.sub.end-V.sub.start, wherein
V.sub.start is the battery voltage at the start of the transition phase
P1 and V.sub.end is the battery voltage at the end of the transition
phase P1. In this example, .DELTA.V is a constant, for example,
.DELTA.V=0.2 Volts.

[0054] F.sub.discharge(V) corresponds to the discharge curve model 140. It
is a function of battery voltage and provides a battery capacity
corresponding to a battery voltage.

[0055] F.sub.charge(V) corresponds to the charge curve model 130 as a
function of battery voltage and provides a battery capacity corresponding
to a battery voltage. According to the transition phase battery capacity
function F1, the battery capacity corresponding to the transition phase
P1 can be calculated. As shown in FIG. 4, the capacity reporting error is
almost within 6% capacity.

[0056] FIG. 5 illustrates an example of a transition battery capacity
model for reporting a battery capacity in a transition phase from
charging state to discharging state. In this example, the transition
battery capacity model is described by a transition battery capacity
function.

[0057] In FIG. 5, a battery 48 is assumed to be charged following curve
130 to voltage of 3.97V corresponding to point 542. Consequently, a 65%
capacity is determined. Next, once the power source is removed, the
battery enters the discharging state, for instance, if a power source 46
of FIG. 2 is disconnected while it is charging the battery 48.

[0058] The battery that has been charging with a voltage reading of 3.97V
may be determined to be 65% full by directly mapping using charging curve
130. If the power source 46 is removed at this point, then the battery's
capacity may erroneously be determined to be 81% full, according to where
3.97V maps on the discharge curve model 140 corresponding to a
discharging state. If that value was reported directly, then the user
would see an incorrect capacity, the battery capacity jumps while the
power source is removed. Actually, the battery takes some time to reach
the discharge curve model 140; that is, there is a transition phase P2
from the charging state to the discharging state. A measured capacity
curve 540 during a transition phase P2 starts at point 542 on the
charging curve model 130 and ends at point 534 on the discharging curve
model 140. A transition battery capacity function F2 corresponding to the
transition phase P2 from the charging to discharging is determined to
report the battery capacity in the transition phase P2 and approaches the
measured curve 540. The determined function F2 curve 550 is used to
report a battery capacity and corresponds to an example transition
battery capacity function F2 curve that starts at point 542 and ends at
point 532. It can be seen from FIG. 5 that the function curve 550 is very
close to the measured curve 540. In fact, the capacity discrepancy error
may fall within 2%. Various transition battery capacity functions F2 may
be provided such that the capacity reporting error may be less than
measured 2%. More complicated functions may more accurately report the
capacity at the expense of higher computational complexity. The capacity
error may be minimized with a complex transition phase battery capacity
function F2. To create a function F2 corresponding to the transition
phase P2 from the charging state to the discharging state, a real
transition phase curve is determined through measurement, then a function
closely mimicking the behavior of the real transition phase curve is
determined as the function F2 in the transition phase P2. A plurality of
transition phase battery capacity functions F2 may be determined and used
to report battery capacity.

[0060] where V is the battery voltage 110 during the transition phase P2
from the charging state to the discharging state.

[0061] F.sub.discharge(V) corresponds to the discharge curve model 140. It
is a function of voltage V. It provides the battery capacity
corresponding to the battery voltage.

[0062] F.sub.charge(V) corresponds to the charging curve model 130. It is
the function of voltage V, and it provides the battery capacity
corresponding to the battery voltage.

[0063] .DELTA.V=V.sub.start-V.sub.end, wherein .DELTA.V defines the
transition phase P2 which is a battery voltage change amount between a
start voltage and an end voltage in the transition phase P2; V.sub.start
is the battery voltage at the start of the transition phase P2, and
V.sub.end is the battery voltage at the end of the transition phase P2.
In this example, .DELTA.V is a constant, for example, .DELTA.V=0.15V.

[0064] Based on the transition phase battery capacity function F2, the
battery capacity corresponding to the transition phase P2 can be
calculated. As shown in FIG. 5, the capacity reporting error is within
2%. The capacity reporting error may be greatly reduced to less than 2%
if other functions are used.

[0065] The transition phase battery capacity functions described provide
examples for the purpose of illustration. It should be understood,
however, that many linear or non-linear functions can be used. If more
complicated functions were used, then the capacity reporting would be
more accurate. The transition phase battery capacity function may be a
function of several factors, including battery voltage, battery charge
curve, and battery discharge curve. It also could be a function of time.
When a transition phase is defined by a time change amount, the
transition phase battery capacity may be a function of time, charging
curve and discharging curve.

[0066] In one example, a plurality of charge curve models, discharge curve
models and transition phase battery capacity models, each having a unique
battery ID, are provided. A charge curve model, a discharge curve model
or a transition phase battery capacity model is selected for determining
battery capacity based on a battery ID.

[0067] In another example, a plurality of charge curve models 130,
discharge curve models 140 and transition phase battery capacity models
wherein each of the models relates to a battery ID and a battery
operating temperature or a temperature range are provided. For example,
models may be provided for battery operating temperatures such as
-20.degree. C., -15.degree. C., -5.degree. C., 5.degree. C., 15.degree.
C., 25.degree. C., 35.degree. C., 45.degree. C. and/or 50.degree. C. or
battery operating temperature ranges of -20.degree. C. to -10.degree. C.,
-10.degree. C. to 0.degree. C., 0.degree. C. to 10.degree. C., 10.degree.
C. to 20.degree. C., 20.degree. C. to 30.degree. C., 30.degree. C. to
40.degree. C. and/or 40.degree. C. to 50.degree. C. A temperature range
such as from -20.degree. C. to 50.degree. C. may be divided into
intervals. For example, an interval size of 5.degree. C. or less may be
used. Alternatively, the temperature range may be divided unevenly. A
charge curve model, a discharge curve model or a transition phase model
corresponding to a temperature closest to the current battery operating
temperature is selected and used to report battery capacity.
Alternatively, a charge curve model, a discharge curve model or a
transition phase battery capacity model corresponding to a temperature
range such as 20.degree. C. to 30.degree. C. containing a current battery
operating temperature such as 24.degree. C. may be selected and used to
report battery capacity.

[0068] The transition phase battery capacity models described above may be
linear or non-linear functions.

[0069] In a further example, instead of providing a plurality of models as
above, a discharge model, a charge model, a transition phase model from
charging to discharging, and a transition phase model from discharging to
charging corresponding to a reference temperature or a reference
temperature range may be provided and set as reference models. The
reference temperature may be a particular temperature such as 22.degree.
C., and the reference temperature range may be a particular temperature
range such as 20.degree. C. to 25.degree. C. A plurality of battery
capacity offsets, wherein each corresponds to a battery ID and a
temperature range or a temperature, are predetermined for compensating
determined battery capacities. If a current battery operating temperature
is a reference temperature or within a reference temperature range, no
temperature compensation is required; that is, a zero battery capacity
offset is applied. Otherwise, a corresponding temperature offset is
applied to a battery capacity reported from a reference model. For
example, when a battery operating temperature is 30.degree. C., a battery
capacity offset 1% is applied to a battery capacity obtained from a
reference model corresponding to a reference range such as 20.degree. C.
to 25.degree. C.

[0070] FIG. 6 is a flowchart illustrating an example method to carry out
step 360 of FIG. 3, according to the transition battery capacity
functions of FIGS. 4 and 5.

[0071] At step 630, a determination is made as to whether the battery is
charging or discharging. For instance, if a battery charging current is
determined, the state can be derived from the sign of the charging
current. At step 630, if it is determined that the battery is being
charged, the process continues to step 620. At step 620, the charging
subsystem 44 determines if the power source 46 is removed while charging
the battery 48, for example, by checking a change in the direction or
sign of battery current. It should be understood that a variety of
methods may be implemented for determining if the battery enters a
transition phase. If the power source 46 is removed, the battery 48
enters a transition phase P2 from charging to discharging, and then at
step 622 a transition phase battery capacity model F2 corresponding to
the transition phase P2, which provides a minimized battery capacity
error, is selected, for example, according to a battery ID.
Alternatively, a different transition phase battery capacity model F2 may
be selected according to the requirements of capacity reporting error and
computational complexity. At step 624, a battery voltage is read, and the
process proceeds to step 626. At step 626, according to the selected
battery capacity model F2 at step 622 and the obtained battery voltage at
step 624, a battery capacity is determined, for example, by calculating
the selected battery capacity model or by looking up a table
corresponding to the selected battery capacity model. A plurality of
tables, wherein each table corresponds to a transition phase battery
capacity model, may be predetermined and pre-stored in memory 24. At step
627, it is determined if the power source 46 is connected. If yes, the
battery enters into another transition phase and the process goes to step
612 and proceeds to the subsequent steps. If no, the process proceeds to
step 628 where a determination is made to see if the transition phase P2
is over. For example, if a battery voltage change amount such as 0.2V is
used to define the transition phase, it is determined that the transition
phase is over when battery voltage is changed by the battery voltage
change amount such as 0.2V from the start of the transition phase. If a
time change amount such as 0.5 hours is used to define the transition
phase, it is determined that the transition phase is over when time is
changed by the time change amount such as 0.5 hours from the start of the
transition phase. If the transition phase P2 is not over, the process
returns to step 624 to read the next voltage for determining the next
battery capacity.

[0072] If the transition phase P2 is over, then step 638 is taken where a
discharge curve model 140 is selected, and a battery voltage is read at
step 639. At step 640, a battery capacity is determined by examining the
discharge curve model, for example by looking up a pre-stored table
corresponding to the discharge curve model. If the power source 46 is not
disconnected while the battery is charging at step 620, the battery 48 is
not in a transition phase, then the process continues to step 634 where a
charge curve model is selected, and a battery voltage is read 635. At
step 636, the charge curve model is applied to determine the battery
capacity based on the read battery voltage, and then the process returns
to step 630 to determine next battery capacity.

[0073] At step 630, if it is determined that the battery is not being
charged, the process continues to step 610. At step 610, it is determined
by the charging subsystem 44 if power source 46 is connected to a battery
48 while the battery 48 is discharging. For example, by checking the
change in the direction or sign of battery current, the charging
subsystem 44 may determine if the power source 46 is connected. It should
be understood that various methods of determining if the battery enters a
charging state. If the answer is yes at step 610, the battery 48 enters a
transition phase P1 from discharging to charging, and the process
proceeds to step 612. At step 612, a transition phase battery capacity
function F1 corresponding to the transition phase P1, which provides a
minimized battery capacity error, is selected, for example, according to
a battery ID. Alternatively, according to the requirements of capacity
reporting error and computational complexity, a different transition
phase battery capacity function F1 may be selected.

[0074] At step 614, a battery voltage value is read and the process
proceeds to step 616. At step 616, according to the selected battery
capacity model F2 at step 612 and the battery voltage at step 614, a
battery capacity is determined, for example, by calculating the selected
battery capacity model or by looking up a table corresponding to the
selected battery capacity model. A plurality of tables, wherein each
table corresponds to a transition phase battery capacity model, may be
predetermined and pre-stored in memory 24. At step 617, it is determined
if the power source 46 is disconnected. If yes, the battery enters into
another transition phase and the process goes to step 622 and proceeds to
the subsequent steps. If no, the process proceeds to step 618. At step
618, it is determined if the transition phase P1 is over. If it is not
over, the process returns to step 614 where the next battery voltage is
obtained for determining the most recent battery capacity.

[0075] If the transition phase P1 is over, then step 634 is taken where a
charge curve model 130 is selected, and a battery voltage is read 635. At
step 636, a battery capacity is determined by examining the charge curve
model, for example by looking up a pre-stored table corresponding to the
charge curve model, and then the process goes to step 630 to determine
the next battery capacity

[0076] Conversely, if at step 610, it is determined that the power source
46 is not connected to the battery 48 while the battery 48 is
discharging, the process goes to step 638 where a discharge curve model
is selected. At step 639, a battery voltage is read. At step 640, a
discharging curve model is used to look up a battery capacity based on
the read battery voltage, and then the process returns to step 630 to
determine the next battery capacity.

[0077] Discharge curve models, charge curve models and transition phase
battery capacity models for determining battery capacity as above may be
pre-stored in memory 24 as lookup tables correlating battery voltage,
battery state and battery capacity. By looking up a table according to a
battery voltage and a battery state, a battery capacity may be
determined.

[0078] Alternatively, the charging curve, discharging curve and transition
phase models may be calculated on the fly by microprocessor 38 using code
stored in memory 24.

[0079] In another example, a plurality of transition phase battery
capacity models wherein each of models corresponds to a predetermined
temperature range is provided so as to minimize battery capacity error.
At step 612, according to a current battery operating temperature, a
transition phase battery capacity model F1 corresponding to the
transition phase P1 is selected from a plurality of transition phase
battery capacity models by determining that the current battery operating
temperature falls into a predetermined temperature range. A similar
process as above is used in steps 622, 634, and 638.

[0080] In a further example, a plurality of transition phase battery
capacity models, each corresponding to a predetermined battery operating
temperature, are provided to more exactly report battery capacity. At
step 612, according to a current battery operating temperature, a
transition phase battery capacity model F1 corresponding to the
transition phase P1 is selected from a plurality of transition phase
battery capacity models by determining that the current battery operating
temperature closest to a predetermined temperature. The selected
transition phase battery capacity model has the predetermined temperature
closest to the current battery operating temperature. A similar process
as above is used in steps 622, 634, and 638.

[0081] In a further example, a plurality of the battery capacity offsets
wherein each of them corresponds to a battery operating temperature range
is provided. According to a current battery operating temperature, the
calculated battery capacity is compensated based on a battery capacity
offset immediately after step 616, by determining if the current battery
operating temperature falls into a predetermined temperature range having
a battery capacity offset. Similarly, immediately after steps 626, 636
and 640, a similar process as above is applied.

[0082] In a further example, a plurality of the battery capacity offsets,
each of them corresponding to a battery operating temperature, is
provided. According to a current battery operating temperature, the
calculated battery capacity is compensated based on a battery capacity
offset immediately after step 616 by determining if the current battery
operating temperature is a predetermined temperature having a battery
capacity offset or the current battery operating temperature is closet to
a predetermined temperature having a battery capacity offset. Similarly,
immediately after steps 626, 636 and 640, a similar process as above is
applied.

[0083] When a battery is in the transition phase from discharging to
charging P1 or the transition phase from charging to discharging P2, the
battery could enter another transition phase if the battery charging
state is changed again. For example, when the battery is connected to a
power source while discharging, it enters into the transition phase from
discharging to charging P1. If the battery is disconnected from the power
source during the transition phase P1, the battery enters into a third
transition phase P.sub.11. A third transition phase model F.sub.11 may be
used to determine a battery capacity. Similarly, when a battery is
disconnected from a power source while charging, it enters into the
transition phase from charging to discharging P2. If the battery is
connected to the power source during the transition phase P2, the battery
enters into a fourth transition phase P.sub.21. A fourth transition phase
model F.sub.21 may be used to determine the battery capacity. F.sub.11
and F1 may be the same function. Similarly, F.sub.21 and F2 may be the
same function.

[0084] The above method may be implemented as an embodiment of charging
subsystem 44. The system may include a transition phase determining
circuitry operatively connected to the battery for determining if the
battery is in a transition phase and battery capacity determining
circuitry operatively connected to transition phase determining circuitry
for determining the battery capacity based on a transition phase battery
capacity model where the battery is in the transition phase. The system
further comprises battery ID determining circuitry operatively connected
to the battery for determining the battery ID, circuitry for selecting a
transition phase battery capacity model from a plurality of transition
phase battery capacity models based on the battery ID, and voltage
reading circuitry operatively connected to the battery for determining a
battery voltage. The system further comprises state determining circuitry
operatively connected to the battery for determining a state of the
battery where the battery is not in the transition phase. The battery
capacity determining circuitry determines the battery capacity by
examining a state curve model correlating voltage, state and capacity
based on the determined charge state. The state includes a charging state
and a discharging state. The state curve model includes a charge state
curve model corresponding to a charging state and a discharge state curve
model corresponding to a discharging state.

[0085] This written description uses examples to disclose the invention,
including the best mode, and also to enable a person skilled in the art
to make and use the invention. The patentable scope of the invention may
include other examples that occur to those skilled in the art.